In recent years, it has been shown that some physical defects, which do not affect the logic behavior of an electronic circuit or device (for instance a CMOS device) usually cannot be detected using voltage oriented test techniques. However, they often reduce the reliability of the circuit. Testing is best performed using a combination of test techniques, with each method dedicated to detect a class of defects. Quiescent power supply current monitoring has been used to detect a variety of such defects See S. McEUEN, “Reliability benefits of IDDQ”, Journal of Electronic Testing: Theory and Applications, Vol. 3, No. 4, December, 1992, pp. 41-49; W. Mao, R. K. Gulati, D. K. Goel and M. D. Cilleti, “QUIETEST: A Quiescent Current Testing Methodology for Detecting Leakage Faults”, Proc. of Inter. Conf. on Computer Aided Design, 1990, pp. 280-283; C. F. Hawkins and J. M. Soden, “Electrical characteristics and testing consideration for gate oxide shorts in CMOS ICs”, Proc. of The 1985 Test Conf, Philadelphia, Pa., 1985, pp. 544-555; W. Maly and M. Patyra, “Built-in Current Testing”, IEEE Journal of Solid State Circuits, Vol. 27, No. 3, March 1992, pp. 425-428.
Nevertheless, the efficiency of Quiescent Current Testing for detecting open defects presents some limitations due to the fact that these failures may prevent changes of the quiescent power supply current. See C. L. Henderson, J. M. Soden and; C. F. Hawkins, “The behavior and testing implications of CMOS IC logic gate open circuits”, Proc. of Inter. Test Conference, November, 1991, pp. 302-310; V. H. Champac, A. Rubio and J. Figueras, “Electrical model of the floating gate defect: Implications on IDDQ testing”, IEEE Trans., 1994, CAD-13 (3), pp. 359-369.
Therefore, the transient power supply current testing (IDDT testing) [S-T. Su and R. Z. Makki, “Testing of SRAMs by Monitoring Dynamic Power Supply Current”, JETTA, Vol. 3, 1992, pp. 265-278.][S-T. Su, R. Z. Makki and T. Nagle, “Transient Power Supply Current Monitoring—A New Test Method for CMOS VLSI Circuits”, JETTA, Vol. 6, February 1995, pp. 23-43.] can be conveniently used to augment the existing test methods and to enhance the defect coverage. On the other hand, the on-chip measurement of the dynamic current presents a more complex issue than performing IDDQ testing.
So far, only a few transient built-in current (BIC) monitors have been proposed See J. Segura, M. Roca, D. Mateo and A. Rubio, “Built-in dynamic current sensor circuit for digital VLSI CMOS testing”, Electronics Letters, Vol. 30, No. 20, September 1994, pp. 1668-1669; J. Arguelles, M. Martinez, and S. Bracho, “Dynamic IDD test circuit for mixed-signal ICs”, Electronics Letters, Vol. 30, No. 6, March 1994, pp. 485-486; Y. Maidon, Y. Deval, J. B. Begueret, J. Tomas, and J. P. Dom, “3.3V CMOS Built-In Current Sensor”, Electronics Letters, Vol. 33, No. 5, February 1997, pp. 345-346.
In the state of the art, no current test monitors not influencing the operation of the DUT (Device Under Test) are available in the context of both static and dynamic (transient) currents and being either on-chip or off-chip.
The Philips Patent Application EP 0386804 A2 shows an arrangement for measuring the quiescent current of a digital circuit wherein the digital circuit under test is incorporated in the branches of a current mirror. Between the supply voltage and the voltage applied to said digital circuit under test an active element is found, resulting in a supplementary voltage drop, influencing the normal operation of the DUT.
The Texas Instruments Patent Application EP 0525421 A2 measures a voltage drop over a test object, and generates a voltage, being the voltage difference over two branches of a three branch current mirror. The connections of two branches of said three branch current mirror are made at an opposite side of the test object and are thus connected to another connection wire. This application further shows an arrangement for observing a voltage change over a test object while forcing a fixed current to flow through said test object. This arrangement thus seeks to measure a change in resistance.